"Conversion was the reason behind the communal riot in Kandhamal in 2007," Justice Panigrahi told reporters here.
At least three persons were killed in the riot which devastated the Kandhamal district during the Christmas week between December 24 and December 27, 2007.
Over 100 churches and church institutions, including convents and hostels, about 700 houses and other structures were burnt in the incident.
Justice Panigrahi Commission, which submitted its findings to Odisha government recently, in its report said though there had been a strong legislation prohibiting religious conversions, that was not implemented leading to communal tension in Kandhamal.
"The local tribals had been tolerating the conversion activities for a long time. But they were strongly opposed to it. Tribals, along with Hindus, were behind the riot. There should be proper coordination between communities in order to avoid such tensions and riots in Kandhamal," Justice Panigrahi said quoting his 560-page report.